Platinum was first introduced into Europe from Colombia in 1735, although the metal was known in America for some time previously[48] p. 608. In 1810 the value of platinum stood at $5 to $6 (U.S.) per oz., and in 1823 the price had further dropped to from $3 to $4 per oz. As a result, platinum was rejected as waste in the operation of refining gold by the “dry-blowing” system. Later, when platinum became valuable, much of this dumped metal was recovered, notably in Quibdo, the capital of the Chocó district, where much gold-refining was carried on. The following table gives the outputs of crude platinum from Colombia, in recent years, principally produced in the Chocó district: Year. Oz. (troy). 1911 12,000 1912 12,000 1913 15,000 1914 17,500 1915 18,000 1916 25,000 1917 32,000 1918 35,000 (estimated) The larger portion of the production is shipped to the United States, the exports to that country for the years 1910–18 being as follows: Year. Oz. (troy). 1910 1,600 1911 5,503 1912 6,627 1913 10,461 1914 12,387 1915 13,121 1916 25,588 1917 21,278 1918 27,030 The crude platinum is estimated at 84 to 85 per cent. fine. The price in 1917 fluctuated from £16 to £20 10_s._ per oz., the average for the year being nearer the latter amount. During 1918 the United States Government fixed the price at $105 per oz., which stimulated production. The deposits are alluvial, and consist of re-concentrates of older gravels. The principal source of supply is at the head of the San Juan River, which enters the Pacific Ocean north of Buenaventura, the richest deposits occurring in the Condoto, Opagado and Tamanal Rivers, tributaries of the San Juan[82]. Platinum is also obtained in the Upper Atrato River, which flows northward to the Caribbean Sea. It is nearly always found associated with gold. In the gravels of the San Juan River the two metals are present in about equal proportions, and in those of the Atrato the ratio is approximately 85 of gold to 15 of platinum.